Question

There is a table with fields: id, name, id_cat
Please show an example of a method that outputs these categories. And where you want to implement this method in the controller or in helpers? Help implement this recursive method.

Answer 1

As I correctly understand you have Category table with circular reference realised by column id_cat.

Following model should works as you expected:

class Category < ActiveRecord::Base
  belongs_to :supercategory, :class_name => "Category", :foreign_key => "cat_id"
  has_many :subcategories, :class_name => "Category", :foreign_key => "cat_id"
end

So if categories table looks like:

id   |   name    |  cat_id
---------------------------
1    | cat 1     | null
2    | cat 1.1   | 1
3    | cat 1.2   | 1
4    | cat 2     | null
5    | cat 1.2.1 | 3

Category.find(1).subcategories returns array with cat 1.1 and cat 1.2 objects.

Category.find(1).supercategory returns nil

Category.find(3).supercategory returns cat 1 object

Category.find(4).supercategory returns nil

…